Driveline lash control method during driver tip-in/out

ABSTRACT

A hybrid electric vehicle has a traction motor, a driveline connected to a vehicle wheel, and a controller. The controller is configured to control motor torque through a region surrounding vehicle wheel torque reversal, control driveline input torque during torque reversal of driveline output torque to limit rate of change of driveline output torque, and control motor torque during a torque reversal of at least one driveline component to limit rate of change of the torque applied to the driveline component. A method for controlling a vehicle having a traction motor includes controlling the traction motor torque through a region surrounding a vehicle wheel torque reversal, controlling driveline input torque during torque reversal of driveline output torque to limit rate of change of output torque, and controlling traction motor torque during a torque reversal of a powertrain component to limit rate of change of the torque applied to the component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional Application No.61/643,612 filed May 7, 2012, the disclosure of which is incorporated inits entirety by reference herein.

TECHNICAL FIELD

Various embodiments relate to a hybrid vehicle and a method ofcontrolling driveline lash for the vehicle.

BACKGROUND

In a vehicle, backlash crossing may occur through the driveline when thewheel torque, or road load torque, and prime mover torque changedirection from one another. The driveline may include the transmissiongear system, driveline joints, and wheels. Lash, or backlash may occurfor example due to lost motion caused by slack or clearance withinvarious driveline components when torque changes direction, such asduring a vehicle acceleration or deceleration event. Ignoring theeffects of backlash crossing results in a disturbance for the driver.

In a conventional vehicle, a slow ramp on engine torque may be used whencrossing the lash zone. Other methods to reduce lash may also be usedincluding spark retard within the engine, which may lead to reduced fuelefficiency and increased torque loading or oscillations on the enginethat contribute to noise, vibration, and harshness (NVH). In a hybridvehicle, controlling crossing the lash zone in the driveline becomesmore complex as there may be more than one prime mover providing torqueto a single input shaft of the driveline. Controlling crossing the lashzone in a hybrid is also more complex as the driveline may be in a driveconfiguration to propel the vehicle or a driven configuration forcharging the battery and/or braking. Detecting or predicting operatingconditions or zones where driveline lash is likely to occur may be usedto mitigate effects of crossing the lash zone.

SUMMARY

In an embodiment, a method for controlling a vehicle having a tractionmotor is provided. The traction motor torque is controlled through aregion surrounding a vehicle wheel torque reversal. The driveline inputtorque is controlled during torque reversal of driveline output torqueto limit rate of change of output torque. The traction motor torque iscontrolled during a torque reversal of at least one powertrain componentto limit rate of change of the torque applied to the powertraincomponent.

In another embodiment, a hybrid electric vehicle is provided with atraction motor, a driveline connected to a vehicle wheel, and acontroller. The controller is configured to control traction motortorque through a region surrounding vehicle wheel torque reversal,control driveline input torque during torque reversal of drivelineoutput torque to limit rate of change of driveline output torque, andcontrol traction motor torque during a torque reversal of at least onedriveline component to limit rate of change of the torque applied to thedriveline component.

In yet another embodiment, a control system for a hybrid vehicle isprovided with a traction motor and a controller. The controller isconfigured to control traction motor torque through a region surroundingvehicle wheel torque reversal, and control traction motor torque duringa torque reversal of at least one driveline component to limit rate ofchange of the torque applied to the driveline component.

As such, various embodiments according to the present disclosure providefor control of backlash in a driveline through the lash zone during avehicle acceleration or deceleration event, such as for a tip in or tipout event. The engine and/or the electric machine are controlleddepending on the operational mode of the vehicle, and whether the inputtorque to the transmission is positive or negative. For electric onlyoperation of the vehicle, the torque output of the electric machine iscontrolled through the lash zone as a ramp or filter function. Forhybrid operation of the vehicle, the torque output of the engine is heldconstant through the lash zone while the torque output of the electricmachine is controlled using a ramp or filter function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a hybrid vehicle capable of implementing anembodiment;

FIG. 2 is a graph illustrating an example of backlash occurring in adriveline;

FIG. 3 is a graph illustrating a model for detecting a lash zone for avehicle;

FIG. 4 is a flow chart illustrating a process for determining a lashzone according to an embodiment;

FIGS. 5 a and 5 b are timing charts illustrating a tip in event and atip out event for a vehicle with no backlash crossing control;

FIGS. 6 a and 6 b are timing charts illustrating a tip in event and atip out event for a vehicle in electric only operation with backlashcrossing control;

FIGS. 7 a and 7 b are timing charts illustrating a tip in event and atip out event for a vehicle in hybrid operation with backlash crossingcontrol; and

FIG. 8 is a flow chart illustrating a process for controlling the effectof backlash crossing in a vehicle.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

FIG. 1 illustrates a schematic diagram of a hybrid vehicle 10 accordingto an embodiment. The vehicle 10 includes an engine 12, and an electricmachine, which, in the embodiment shown in FIG. 1, is a motor generator(M/G) 14, and alternatively may be a traction motor. The M/G 14 isconfigured to transfer torque to the engine 12 or to the vehicle wheels16.

The M/G 14 is connected to the engine 12 using a first clutch 18, alsoknown as a disconnect clutch or the upstream clutch. A second clutch 22,also known as a launch clutch or the downstream clutch, connects the M/G14 to a transmission 24, and all of the input torque to the transmission24 flows through the launch clutch 22. Although the clutches 18, 22 aredescribed and illustrated as hydraulic clutches, other types ofclutches, such as electromechanical clutches may also be used.Alternatively, the clutch 22 may be replaced with a torque converterhaving a bypass clutch, as described further below. In differentembodiments, the downstream clutch 22 refers to various coupling devicesfor the vehicle 10 including a traditional clutch, and a torqueconverter having a bypass (lock-out) clutch. This configuration may usean otherwise conventional automatic step-ratio transmission with atorque converter and is sometimes referred to as a modular hybridtransmission configuration.

The engine 12 output shaft is connected to the disconnect clutch 18,which in turn is connected to the input shaft for the M/G 14. The M/G 14output shaft is connected to the launch clutch 22, which in turn isconnected to the transmission 24. The various components of the vehicle10 are positioned sequentially in series with one another. The launchclutch 22 connects the vehicle prime movers to the driveline 26, whichincludes the transmission 24, differential 28, and vehicle wheels 16,and their interconnecting components. In other embodiments, the methoddescribed herein may be applied to hybrid vehicle having other systemarchitectures.

In another embodiment of the vehicle 10, the downstream clutch 22 is abypass clutch with a torque converter. The input from the M/G 14 is theimpeller side of the torque converter, and the output from the torqueconverter to the transmission 24 is the turbine side. The torqueconverter 22 transfers torque using its fluid coupling, and torquemultiplication may occur depending on the amount of slip between theimpeller and turbine sides. The bypass or lock-up clutch for the torqueconverter may be selectively engaged to create a mechanical orfrictional connection between the impeller side and the turbine side fordirect torque transfer. The bypass clutch may be slipped and/or openedto control the amount of torque transferred through the torqueconverter. The torque converter may also include a mechanical lockupclutch.

In the vehicle 10, the launch clutch 22 or bypass clutch for the torqueconverter may be locked to increase fuel efficiency, and may be lockedwhen crossing a lash zone during a tip in or tip out event. Thedriveability and control of the effect of lash crossing within thedriveline depends on the control of the powertrain torque from theengine 12 and/or the electric machine 14. M/G 14 torque may becontrolled to a greater accuracy and with a faster response time thanengine 12 torque. During an electric-only mode of operation for thevehicle 10, the M/G 14 torque may be controlled when crossing a lashzone. During a hybrid mode of operation of the vehicle with both theengine 12 and M/G 14 operating, the M/G 14 torque and engine 12 torquemay be controlled together in order to improve driveability of thevehicle 10 and reduce the effect of lash crossing in the driveline.

In the representative embodiment illustrated, the engine 12 is a directinjection engine. Alternatively, the engine 12 may be another type ofengine or prime mover, such as a port injection engine or fuel cell, oruse various fuel sources, such as diesel, biofuel, natural gas,hydrogen, or the like. In some embodiments, the vehicle 10 also includesa starter motor 30 operatively connected to the engine 12, for example,through a belt or gear drive. The starter motor 30 may be used toprovide torque to start the engine 12 without the addition of torquefrom the M/G 14, such as for a cold start or some high speed startingevents.

The M/G 14 is in communication with a battery 32. The battery 32 may bea high voltage battery. The M/G 14 may be configured to charge thebattery 32 in a regeneration mode, for example when vehicle power outputexceeds driver demand, through regenerative braking, or the like. TheM/G 14 may also be placed in a generator configuration to moderate theamount of engine 12 torque provided to the driveline 26. In one examplethe battery 32 is configured to connect to an external electric grid,such as for a plug-in hybrid electric vehicle (PHEV) with the capabilityto recharge the battery from an electric power grid, which suppliesenergy to an electrical outlet at a charging station. A low voltagebattery may also be present to provide power to the starter motor orother vehicle components, or low voltage power may be provided through aDC to DC converter connected to the battery 32.

In some embodiments, the transmission 24 is an automatic transmissionand connected to the drive wheels 16 in a conventional manner, and mayinclude a differential 28. The vehicle 10 is also provided with a pairof non-driven wheels, however, in alternative embodiments, a transfercase and a second differential can be utilized to positively drive allof the vehicle wheels.

The M/G 14 and the clutches 18, 22 may be located within a motorgenerator case 34, which may be incorporated into the transmission 24case, or alternatively, is a separate case within the vehicle 10. Thetransmission 24 has a gear box to provide various gearing ratios for thevehicle 10. The transmission 24 gearbox may include clutches andplanetary gearsets, or other arrangements of clutches and gear trains asare known in the art. In alternative embodiments, the transmission 24 isa continuously variable transmission or automated mechanicaltransmission. The transmission 24 may be an automatic six speedtransmission, other speed automatic transmission, or other gearbox as isknown in the art.

The transmission 24 is controlled using a transmission control unit(TCU) 36 or the like to operate on a shift schedule, such as aproduction shift schedule, that connects and disconnects elements withinthe gear box to control the gear ratio between the transmission outputand transmission input. The gear ratio of the transmission 24 is theideal torque ratio of the transmission 24. The TCU 36 also acts tocontrol the M/G 14, the clutches 18, 22, and any other components withinthe motor generator case 34.

An engine control unit (ECU) 38 is configured to control the operationof the engine 12. A vehicle system controller (VSC) 40 transfers databetween the TCU 36 and ECU 38 and is also in communication with variousvehicle sensors. The control system 42 for the vehicle 10 may includeany number of controllers, and may be integrated into a singlecontroller, or have various modules. Some or all of the controllers maybe connected by a controller area network (CAN) or other system. Thecontrol system 42 may be configured to control operation of the variouscomponents of the transmission 24, the motor generator assembly 34, thestarter motor 30 and the engine 12 under any of a number of differentconditions, including in a way that minimizes or reduces the effect oflash crossing in the driveline 26 and impact on the driver during tip inor tip out events.

Under normal powertrain conditions (no subsystems/components faulted),the VSC 40 interprets the driver's demands (e.g. PRND and accelerationor deceleration demand), and then determines the wheel torque commandbased on the driver demand and powertrain limits. In addition, the VSC40 determines when and how much torque each power source needs toprovide in order to meet the driver's torque demand and to achieve theoperating points (torque and speed) of the engine 12 and M/G 14.

The vehicle 10 may have speed sensors 44 positioned at various locationsof the powertrain and driveline 26. The speed sensors 44 provideinformation to the control system 42 regarding the rotational speed of ashaft in approximately real time, although there may be some lag due toresponse time, and signal and data processing. In the embodiment shownin FIG. 1, there is a speed sensor 44 that measures the speed of theengine 12 output shaft, the speed of the shaft connected to the M/G 14,the speed of the transmission 24 input shaft, the speed of thetransmission 24 output shaft, and the speed of one or both of the axlesconnected to the wheels 16.

As a part of the control strategy or algorithm for operation of thevehicle 10, the control system 42 may make an engine 12 torque request(τ_(e)) and/or a M/G 14 torque request (τ_(m)), as shown in FIG. 1. Thenet transmission input torque (τ_(i)) is composed of the electric motortorque and engine torque (τ_(i)=τ_(m)+τ_(e)), assuming that thedisconnect and launch clutches 18, 22 are locked.

In alternative embodiments, the clutch 22 may be replaced with a torqueconverter unit including a torque converter and a lockup clutch orbypass clutch. The torque converter has torque multiplication effectswhen certain rotational speed differentials exist across the torqueconverter. During torque multiplication, the output torque of the torqueconverter is larger than that of the input torque due to torquemultiplication across the torque converter. Torque multiplication existsfor example, when the vehicle 10 is started from rest and the inputshaft to the torque converter begins to rotate, and the output shaftfrom the torque converter is still at rest or has just begun to rotate.

The lockup clutch or bypass clutch is used to lock out the torqueconverter such that the input and output torques for the downstreamtorque transfer device 22 are equal to one another, and the input andoutput rotational speeds for the device 22 are equal to one another. Alocked clutch eliminates slipping and driveline inefficiency across thetorque converter, for example, when the rotational speed ratio acrossthe torque converter is greater than approximately 0.8, and may increasefuel efficiency for the vehicle 10.

Changing torque amounts and/or directions may cause disturbances oroscillation in driveline 26 associated with lash crossing. Backlash mayoccur in a vehicle driveline 26 whenever one of the wheel 16 torque andpower plant 12, 14 torque change direction from the other. This changein torque direction may occur with the vehicle 10 operating with boththe disconnect clutch 18 and the launch clutch 22, or lock out clutchfor the torque converter, in a locked or engaged position. For example,when vehicle 10 is decelerating, the compression braking effect of theengine 12 provides negative torque to the transmission 24 which is thenpassed through the differential 28 and then to the wheels 16. At thispoint, the driveline 26 is wrapped in the negative direction. If thedriver provides a power request, or tip in, using the accelerator pedal,the engine 12 torque switches from negative to positive as it begins tosupply torque to propel the vehicle 10 forward. The driveline 26unwraps, as each driveline component changes from transmitting negativetorque to transmitting positive torque. At some point during thistransition, the driveline 26 passes through a relaxed state with zerotorque applied to the wheels 16.

During this zero torque region, gear teeth in the transmission 24 and/ordifferential 26 may not be tightly coupled with their mating gears andthere may be some play in the driveline 26. Play across multiple sets ofgears acts as cumulative. As the engine 12 continues to provide positivetorque, the driveline 26 will wrap in the positive direction. The gearsmay be quickly coupled resulting in a clunk. Also, the axle connectingthe differential 26 to a wheel 16 may twist slightly as a result ofhigher torque on the differential 26 side of the axle compared to thewheel 16 side. The axle may act as a torsional spring to store thisenergy. As the vehicle 10 begins to accelerate, the wheel 16 torquecatches up to the torque at the differential 26, and any energy storedin the axle is released quickly causing an oscillation in the oppositedirection, or backlash. The result of this backlash crossing is a clunkor noise when the gear teeth hit together, and a reduction in wheeltorque when the axle energy is expended. The clunks and oscillations maybe noticed by a driver depending upon their severity. For a drivelinewith multiple gear meshes arranged in series, each gear mesh may have alash zone. The lash in the driveline cascades or progresses through thegear meshes. After a gear mesh is engaged, the subsequent gear meshcrosses through a lash zone as the torque reversal goes through.Backlash may include main gear lash as well as any subsequent gears.

The scenario described above can also happen in the opposite direction.In this case, the driver would be providing a power request, such as atip in of the accelerator pedal for vehicle acceleration, and thensuddenly removing the power request by releasing the accelerator pedalthrough a tip out. The driveshaft 26 goes from being wrapped in thepositive direction to being wrapped in the negative direction, with asimilar torque dip or hole and clunk during the transition. The effectof the backlash crossing due to sudden acceleration is typically morenoticeable than sudden deceleration.

Two backlash conditions for the vehicle 10 are shown graphically in FIG.2 as an example. The accelerator pedal 60, transmission output speed 62,wheel speed 64, and wheel torque 66 are shown during a suddendeceleration at 68 and acceleration at 70. After the decelerationrequest at 68, transmission output speed 62 decreases faster than thewheel speed 64. This leads to the region 72 labeled “zero wheel torque”,where the driveline 26 is in its relaxed state as wheel torque 66 makesa transition from positive to negative. Immediately following thistransition, the wheel torque 66 decreases rapidly as the wheel speed 64catches up to the transmission output speed 62, which leads into theregion 74 labeled “torque dip”. This torque dip 74 is essentially thebacklash, and is caused by the energy stored in the half shaft beingreleased and the play in the transmission 24 and other drivelinecomponents, in addition to the negative torque supplied by thetransmission output. The effect of the backlash crossing 74 causes aresultant oscillation in the wheel torque.

During acceleration after a tip in request at 70, a similar scenariooccurs, only in reverse. The increase in transmission output speed 62leads to the increase in wheel speed 64, which leads into the zerotorque region 76 and then a rapid torque rise or “torque spike” at 78,causing a backlash crossing effect, or a noise and oscillation which maybe felt by the driver.

The control system 42 is configured to detect, sense, and/or predict thelash region to reduce or mitigate the effect of the backlash crossing.The backlash in the vehicle 10 may be sensed by observing transmissioninput and output torque ratio, as described below. In other embodiments,backlash may also be sensed by using speed sensors, or other techniquesas are known in the art.

FIG. 3 shows the ratio of input torque to output torque across thetransmission 24. An ideal or perfect transmission 24 has a perfecttorque ratio as shown by line 100 crossing through zero. However, thereare proportional and non-proportional losses in a real transmission 2that should be accounted for. The losses have the effect of transposingor modifying the ideal torque ratio to an actual ratio of output torqueto input torque. The actual torque ratio is the ideal torque ratio withthe addition of losses. When input and output torques are both negative(generating), the transmission losses act to assist the vehicle inslowing down. When input and output torque are positive (propulsion),the losses impede propulsion effort. Line 118 represents the actualratio during propulsion, taking losses into account. Line 120 representsthe actual ratio when generating, taking losses into account. Line 122is the range of ratios where the transmission 24 is carrying near-zerotorque, and the potential for the effect of the lash zone to occur isthe highest, and line 122 represents the lash region.

Region 124 represents the entry region for the lash zone from thepropulsion, or positive input torque side. Region 126 represents theentry where entry region for lash from the generating, or negative inputtorque side. Notice that the line 122 between regions 124 and 126 isbounded by an input torque of zero (at 126) to an input torque of ascalar quantity (at 124). In other embodiments, other boundaries may beset to define the lash zone. By controlling input torque when thevehicle 10 is operating on line 122 as the vehicle accelerates ordecelerates along it, the effects of a lash crossing event may bereduced or mitigated. The line 122 may be linear or nonlinear. Forexample, line 122 may be a step function with multiple steps cause bylash in each gear mesh in the driveline.

The input to output torque model for a gear ratio as illustrated in FIG.3 may be determined as described below. During acceleration events, thedriveline is in a drive configuration, such that torque from the engineand/or the M/G 14 is transmitted to the wheels 16 through thetransmission 24. During deceleration events, the driveline is in adriven configuration, such that torque from the wheels 16 is transmittedto the M/G 14 through the transmission 24. However, the amount of torquetransmitted through the transmission 24 and driveline 26 is a functionof the gear ratio and losses in the transmission 24 and driveline 26.FIG. 3 illustrates the torque, gear ratio and losses of the transmission24 graphically. The gear ratio of the transmission 24 is equal to aratio of the torque input (τ_(in)) and torque output (τ_(out)), whereτ_(in) is the torque at the input shaft 46 to the transmission 24 andτ_(out) is the torque at the output shaft 48 of the transmission 24 andthere are no losses in the system. The gear ratio may be based on aspeed ratio, and be directly calculated directly from the numbers ofteeth of the various gears that are engaged in the transmission 24. Thegear ratio may also be considered an ideal torque ratio. For example, ifthe gear ratio is 4:1, for a +100 Nm (Newton-meter) input torque(τ_(in)), the output torque (τ_(out)) is 400 Nm. Therefore, the idealtorque ratio is represented by line 100 in FIG. 3 where the slope of theline is the ideal torque ratio, or the gear ratio.

A linear relationship may be used to relate torque input to torqueoutput for a transmission, where the linear line can be described withthe formula:y=m*x+b

where y is the output torque (τ_(out)) and x is the input torque(τ_(in)). The slope, m, is the torque ratio output/input or the gearratio, and b is the output torque when the input torque is zero.

Ideally, or in a transmission 24 without losses, the slope would be theideal torque ratio and the offset is zero, as shown by line 100. Theslope with no losses is the ideal torque ratio or gear ratio(TR_(ideal)). Therefore, the formula for the line 100 is:τ_(out)=(τ_(in)*TR_(ideal))  Equation (1)

However, the transmission 24 is not perfectly efficient and has somelosses. The losses in the transmission may be a function of friction,heat, spin losses or many other factors. The losses in the transmissionmay be characterized as ‘proportional losses’ and ‘non-proportionallosses’. Proportional losses vary as a function of the current gear andspeed, whereas non-proportional losses are independent of torque. Theefficiency for a transmission 24 is usually measured across thetransmission 24. The driveline 26 efficiency is typically measured withthe launch clutch 22 locked or the bypass clutch for a torque converterlocked, or may be modeled without a torque converter.

The intercept b is equal to the non-proportional loss, T_(s),illustrated at 112 in FIG. 2 for each gear for a step gear transmission.Line 114 illustrates the ideal torque ratio or gear ratio whenaccounting for non-proportional losses, T_(s), in the transmission 24.Non-proportional losses, Ts, may be in units of output torque. Thenon-proportional losses, or spin losses, in the driveline may be afunction of driveline output speed, driveline oil temperature, and whatgear the driveline is in. The driveline output speed may be a functionof driveline input speed and agear ratio of the driveline. Therefore,the formula for line 114 is:τ_(out)=(τ_(in)*TR_(ideal))−T _(s)  Equation (2)

Proportional transmission losses should also be accounted for in themodel. The actual torque ratio of the transmission 24 of τ_(out) toτ_(in) can be measured empirically in different gears. The empiricalmodeling of the transmission 24, without the torque converter 22(locked, or not included), allows for representation of the‘proportional to torque’ losses separate from ‘non-proportional totorque’ losses, which may be represented by using a linear relationshipbetween output torque and input torque. Proportional losses may be afunction of the driveline oil temperature, what gear the driveline isin, and the input torque to the driveline. Proportional losses arerepresented by the slope of the output to input torque relationship foreach gear. The slope including proportional losses is equal to theactual torque ratio across the transmission 24. By knowing the idealtorque ratio, or gear ratio, and torque input-output relationship andmeasuring only a few points of the actual torque ratio input-outputrelationships, the difference between the slopes of the ideal torqueratio (TR_(ideal)) and the actual torque ratio (TR_(actual)) can bedetermined. By subtracting off the portion of τ_(in) that comes from thedifference in the slopes between the ideal torque ratio and the actualtorque ratio, we can account for the proportional torque losses.Non-proportional losses are represented by T_(s). The linear formula forthe transmission when accounting for proportional and non-proportionallosses, shown as line 116 in FIG. 2, could be written as:τ_(out)=(τ_(in)*TR_(ideal))−T_(s)−τ_(in)*(TR_(ideal)−TR_(actual))  Equation (3A)

Cancelling out the terms in the right hand side of the loss equation,the formula for line 116 in FIG. 3 may be simplified to:τ_(out)=(τ_(in)*TR_(actual))−T _(s)  Equation (3B)

For example, with a +100 Nm input torque, actual torque ratio of 4.0,ideal torque ratio of 4.1, and non-proportional loss of 5, the τ_(out)may be determined as follows. Note that the numbers are truncated forsimplicity in the example.

First, using Equation (3A), the output torque is calculated as:τ_(out)=(100*4.1)−5−(100*(4.1−4.0))=395 Nm

Using Equation (3B), the output torque is calculated as:τ_(out)=(100*4.0)−5=395 Nm

Power can be determined multiplying torque by the speed of the shafts46, 48, illustrated by the equation:P=τ*ω

Using an input speed of 400 rad/sec, we can determine the powercalculations.P _(in)=100*400=40,000 WattsP _(out)=395*(400/4.1)=38,536 Watts

The difference between the power at the transmission input 46 and thetransmission output 48 is the amount of power loss because oftransmission inefficiencies.P _(in) −P _(out)=1,464 Watts

The loss formulas in Equation (3) are generally accurate in describingthe transmission including losses in a traditional powertrain. The lossformulas in Equation (3) can also accurately describe the transmissionincluding losses in a HEV powertrain when the vehicle 10 is motoring.However, an issue arises when the vehicle 10 is putting power into thetransmission output 62 and extracting it from the transmission input 60,such as during regenerative powertrain braking in a HEV. In thissituation, the torque values through the driveline 26 are negative, thetransmission is in a driven configuration, and the loss formulas inEquation (3) apply differently.

The issue with the loss formulas in Equation (3) during regenerativepowertrain braking is illustrated by another example as shown below. Forexample, for negative torques, where the input torque τ_(in) is −100 Nminput torque, the actual ratio is 4.0, the ideal ratio is 4.1, andnon-proportional losses (T_(s)) is 5, τ_(out) is calculated as:τ_(out)=(−100*4.1)−5−(100*(4.1−4.0))=−405 Nm,using Equation (3A), orτ_(out)=(−100*4.0)−5=−405 Nm,using Equation (3B).

Using an input speed of 400 rad/sec, we can determine the powercalculations as:P _(in)=−100*400=−40,000 WattsP _(out)=−405*(400/4.1)=−39,512 WattsP _(in) −P _(out) =P _(loss)=−488 Watts

Using the standard formulas arrives at a negative loss calculation,which is not possible, as the power going into the output shaft 48 ofthe transmission 24 is smaller than the power coming out through theinput shaft 46 of the transmission during. For this example, 40,000Watts of regenerative energy are collected at the transmission input 46when only 39,512 Watts of regenerative energy is going into thetransmission output 48 from the wheels 16.

For modeling the torque relationship, two lines fit the data better thanone line. The first line, illustrated as line 118 in FIG. 3, is forpositive output torque τ_(out) and input torque τ_(in), such as when thevehicle 10 is motoring. The second line, illustrated as line 120 in FIG.2, is for negative output torque and input torque, such as when thevehicle 10 is regenerative braking.

The non-proportional losses 112 are calculated the same during motoringand regeneration. Therefore, line 118 and line 120 both use the sameoffset term b for non-proportional torque loss T_(s). However, duringregeneration, the proportional losses are not correctly accounted forusing the standard motoring equations.

The correct τ_(in) for a given τ_(out) value is correctly computed whenthe proportional torque losses are summed in the correct direction. Theproportional loss term in Equation (3A), that isτ_(in)*(TR_(ideal)−TR_(actual)), must be a positive value, regardless ifthe transmission is transmitting positive or negative torque. Becauseτ_(in) is negative during regeneration and the proportional lossexpression in Equation (3A) must be positive, the ideal torque rationeeds to be less than actual torque ratio during regeneration in orderto provide the correct calculation that more energy is going into thetransmission output 48 than is received at the transmission input 46during negative torque transfer.

For example, during a negative torque transmission, where thetransmission input torque τ_(in) is −100 Nm, the actual torque ratio is4.2, the ideal torque ratio, being less than the actual ratio, is 4.1,and non-proportional losses T_(s) is 5, τ_(out) can be determined as:τ_(out)=(−100*4.1)−5−(−100*(4.1−4.2))=−425 Nm,using Equation (3A), orτ_(out)=(−100*4.2)−5=−425 Nm,using Equation (3B).Note that the previous loss of −405 is approximately five percent inerror.

Using an input speed of 400 rad/sec, the power may be calculated:P _(in)=−100*400=−40,000 WattsP _(out)=−425*(400/4.1)=−41,463 WattsP _(in) −P _(out) =P _(loss)=1463 Watts

When the output torque and input torque are both positive the actualmeasured slope is less than the ideal torque ratio, as seen by line 118compared to line 114. However, when the output torque and input torqueare both negative, the actual measured slope, or TR_(actual) is greaterthan the mechanical torque ratio, or TR_(idea), as seen by line 120compared to line 114. The actual torque ratio for negative torque ismeasured to be 4.2. If the measured positive torque ratio of 4.0 is usedfor the negative torque situation, then Equation (3) will calculate thatmore energy is being collected at the transmission input 60 than isbeing input into the transmission output 62 during regeneration (asshown by line 116 compared to line 114).

To account for the difference between the actual torque ratio and theideal torque ratio (or gear ratio), a proportional loss coefficient C1is calculated for each gear using the following formula:C1=τ_(in)*(TR_(ideal)−TR_(actual))  Equation (4)

During propulsion/motoring, or positive torque through the transmission24, the proportional loss coefficient C1 is included in Equation (3B) toderive the loss equation as follows:τ_(out)=(τ_(in)*(TR_(actual) −C1))−T _(s)  Equation (5)

Or alternatively, Equation (5) may be rearranged to determine a τ_(in)based on a desired torque output τ_(out) during motoring as:τ_(in)=(τ_(out) +T _(s))/(TR_(ideal) −C1)  Equation (6)

When the torque through the transmission 24 is negative, such as duringa regenerative braking event, the actual torque ratio is greater thanthe ideal torque ratio (or gear ratio) by the same amount that the idealtorque ratio is greater than the actual torque ratio during motoring.Therefore, the sign of C1 changes during regenerative braking, but theabsolute value of C1 remains the same. Therefore during negative torquetransfer through the transmission, the τ_(in) based on a desired torqueoutput τ_(out) is:τ_(in)=(τ_(out) +T _(s))/(TR_(ideal) +C1)  Equation (7)

The input to output torque relationship for the transmission 24 istherefore better characterized by two lines 118, 120 to differentiatebetween motoring and regeneration, or positive and negative torque. Line120 in FIG. 3 illustrates the line accounting for proportional losseswhich add to regenerative braking. Line 120 may be characterized byrearranging Equation (7) as:τ_(out)=(τ_(in)*(TR_(ideal) +C1))−T _(s)  Equation (8)

The inclusion of a torque converter, pump losses, and dynamic inertialosses can be consistent across the transmission controls developmentprocess. For example, when the vehicle includes a torque converter 22,the torque input τ_(in) when the vehicle is motoring may be determinedas:τ_(in)=((τ_(out) +T _(s))/(TR_(ideal) −C1))*(1/TR_(torque) _(—)_(converter))+Loss_(pump)+Loss_(dyn) _(—) _(inertia)  Equation (9)

When the M/G 14 is generating or when the vehicle is regenerativebraking such that the transmission output torque is negative, Equation(9) is modified so that the torque input τ_(in) may be determined fromthe following equation:τ_(in)=((τ_(out) +T _(s))/(TR_(ideal) +C1))*(1/TR_(torque) _(—)_(converter))Loss_(pump)+Loss_(dyn) _(—) _(inertia)  Equation (10)

The torque converter 56 may be connected between the M/G 14 and thetransmission 24. The torque converter 56 may also be included in thetransmission 24. When the torque converter 56 is locked, the torqueratio of the torque converter is 1:1.

The control system 42 is configured to determine a lash zone for thevehicle based on the gear of the transmission, and to use the determinedlash zone during vehicle operation to predict or detect an impendinglash zone, which may in turn be used in a control strategy to mitigatethe effect of the driveline lash crossing.

First, the controller 42 receives a vehicle torque request at 150, suchas a torque request from the driver through a tip in or tip out event.The vehicle torque request is a request for a wheel torque, whichrelates to τ_(out). The controller 42 converts τ_(out) to τ_(in) basedon the ideal torque ratio of the transmission 24, as represented byblock 152.

The controller 42 determines the value for the current gear, oralternatively the actual torque ratio, as represented by block 156. Theactual torque ratio may be stored in a lookup table which corresponds tothe current gear, or corresponds to whether the vehicle is motoring orregenerative powertrain braking, as described above.

The actual torque ratio is used with the transmission speeds, eitherestimated or actual, to determine the non-proportional loss, asrepresented by block 154. The non-proportional loss values may be storedin a lookup table which corresponds to the current gear and is accessedor indexed by the transmission speeds, as described above when latercalculating the actual torque ratio 156.

The controller 42 determines the torque proportional loss, asrepresented by block 158 of FIG. 4. The proportional loss values mayalso be stored in a lookup table with a separate set of values for eachof the available gears or torque ratios, as well as negative torquevalues or positive torque values.

Block 160 represents determination of a proportional loss coefficientbased on the currently selected gear. This factor may be used tofine-tune or calibrate the torque determination for any additionallosses which may not be included in the torque loss terms describedabove.

The controller 42 then determines at 162 whether the torque is in apositive or negative direction through the transmission and driveline,i.e. whether the vehicle is motoring or generating/braking, or whetherthe driveline is in a drive configuration or driven configuration. Ifthe vehicle 10 is motoring with the driveline in a drive configuration,or has positive torque flowing from the engine 12 and/or M/G 14 to thewheels 16, the controller 42 proceeds to 164 to calculate the τ_(in)using Equation (6). The entry point to the lash zone is calculated atblock 166 by calculating the τ_(in) when τ_(out) is zero, or anotherdesignated value.

If the vehicle 10 is generating/braking with the driveline in a drivenconfiguration, or has torque flowing from the wheels 16 to the engine 12and/or M/G 14, the controller 42 proceeds to 168 to calculate the τ_(in)using Equation (8). The entry point to the lash zone is calculated atblock 170 by calculating the τ_(out) (or torque input to the drivelineor transmission) when τ_(in) is zero, or another designated value.

The lash zone entry points from 166 and 170 are used at block 172 toprovide a lash zone to the control system 42 for use in a backlashcrossing control algorithm.

Lash zone crossing control may be handled differently by a controlalgorithm based upon whether the engine 12 is off such that the vehicle10 operates in an electric-only mode, or the engine 12 is on, such thatthe vehicle operates in a hybrid mode with the M/G 14 also operating. Inthe engine-off case, the only actuator is the M/G 14, so nettransmission input torque, τ_(in), is equal to the motor torque. In theengine-on case, there are two actuators acting upon the transmissioninput shaft, so the net transmission input, τ_(in), is equal to the M/G14 torque plus the engine 12 torque. Thus, only motor 14 torque iscontrolled in electric drive whereas both motor torque and engine torqueare controlled and blended in a hybrid drive.

The M/G 14 may provide better control crossing through the lash zonethan the engine 12. The improved control is more apparent in thedeceleration case because the engine 12 is typically controlled usingspark retard or a similar technique. The M/G 14 generally has goodauthority near zero torque and/or around zero or near zero speeds. TheM/G 14 has a faster response time than the engine 12, which may lag dueto throttle response, and the like. Additionally, the M/G 14 may havemore accurate control over the amount of torque provided by it comparedto the engine 12.

FIG. 5 illustrates an example of input torque and output torque during alash crossing event with no control in place to mitigate any lashcrossing effect. In the tip-in case in FIG. 5 a, a command for tip-in isshown at 200. The input and output torques 202, 204 are going from anegative value, i.e. charging, regeneration or cruise, to a positivevalue with propulsion or motoring. As the net input torque 202 goesthrough the lash 206 region from R1 to R2, the gears in the transmissionand driveline are relaxed and torque does not increase linearly at theoutput as shown by 208. When R2 is reached at the end of the lash zone206, the gears mesh suddenly, causing a surge in output torque at 210.The surge winds the driveline up like a spring, and then the springenergy is released causing a resulting oscillation at 212.

A similar phenomenon happens during the tip-out case shown in FIG. 5 bwith no lash crossing control. During tip-out as shown by a tip outcommand on line 214, the input and output torques 216, 218 go frompositive, i.e. propulsion or motoring, to negative, i.e. charging orregeneration. As the net input torque 216 goes through the lash 220region from R1 to R2, the gears in the transmission and driveline arerelaxed. When R2 is reached at the end of the lash zone 220, the gearsmesh suddenly, causing a downward surge in output torque at 222. Thesurge winds the driveline up like a spring in the opposite directioncompared to FIG. 5 a, and then the spring energy is released causing aresulting oscillation at 224.

FIG. 6 shows a lash crossing event while the engine 12 is off, withmotor 14 torque control used to mitigate the lash event in a tip in casein FIG. 6 a and a tip out case in FIG. 6 b. The net input torque to thetransmission 24 is equal to the motor 14 torque since the engine 12 isoff. The engine 12 may be disconnected with the disconnect clutch 18opened. During the tip-in event at 250 in FIG. 6 a, the motor torque 252rises quickly as driver demand increases until input torque point R1 isreached. From R1 to R2, within the lash zone 254, the motor torque 252is increased slowly as a ramp or filter function until net input torquereaches R2. Although motor torque 252 is shown as a line across 254, themotor torque 252 may be modulated to any desired profile, and in oneembodiment is provided from a two dimensional look up table with atailored response for the vehicle.

After the lash region 254, normal torque control is resumed, with a fastramp or filter to bring the torque 252 up to driver demand in a smoothfashion. By controlling the rise or charge in input torque 252 throughthe lash region 254, the transmission 24 is walked through its relaxedstate, which slowly brings the gear teeth in one or more gear meshestogether from the relaxed state, and little or no clunk occurs, as shownby the output torque 256. Once the gear teeth are meshed at R2, moremotor torque 252 may be applied without a harsh event and the resultingharsh oscillation.

A similar type of control crossing through a lash region is used in thetip-out case in FIG. 6 b. After a tip out event at 260, the motor torque262 is reduced quickly to meet driver demand or charge/regenerationdemand until point R2 is reached. From R2 to R1, within the lash zone264, the torque 262 is controlled in a slow ramp or filter functionuntil point R1 is reached. The motor torque 262 may be controlled to anyprofile through the lash region 264. In one embodiment, the motor torque262 is rapidly decreased by a large amount before the lash zone 264, andis reduced by a much smaller amount through the lash zone to control andreduce lash in the driveline. At point R1, the gear teeth are meshed,and more motor torque 262 may be applied in the negative directionwithout a harsh event or oscillation, as shown by the smooth outputtorque 266.

FIG. 7 shows a lash crossing event while the engine 12 is on and thevehicle 10 is operating in a hybrid mode. In this case, the net inputtorque is equal to the motor 14 torque plus the engine 12 torque. Thus,it is necessary to control both motor 14 and engine 12 torque tomitigate a lash crossing event. Since the M/G 14 has a faster responsetime and more accurate control over the torque provided, the M/G 14torque generally leads through the lash region and the engine 12 torqueis generally held. The engine 12 torque is commanded to a constant orgenerally constant value while the motor 14 torque is modulated toachieve the desired effect in net transmission input torque. During thelash region of R1 to R2, the motor torque response leads the enginetorque response in both the tip-in and tip-out cases.

During the tip-in event at 300 shown in FIG. 7 a, the motor torque 302rises quickly as driver demand increases until input torque point R1 isreached for the net input torque 304. The motor torque 302 is typicallylifted up quickly to meet driver demand, and leads any rise in enginetorque response from the throttle, which is referred to as torquetransient filling. From R1 to R2, within the lash zone 306, the enginetorque 308 is commanded to be generally constant and the motor torque302 is increased slowly as a ramp or filter function to control thetorque across the lash zone until net input torque reaches R2 and thegear teeth are smoothly meshed. Of course, the motor torque 302 may becommanded to any profile to correspond with the engine torque 308 and tocontrol torque through the lash zone 306. After the lash zone 306,normal torque control is resumed, with engine torque 304 rising up todriver demand in a smooth fashion. Notice that the output torque 310does not have any noticeable backlash.

During a tip-out event 350, illustrated in FIG. 7 b, the engine torque352 is reduced quickly to meet driver demand until the input torquepoint R2 is reached. From R2 to R1, within the lash zone 354, the enginetorque 352 is held constant at a nominal or other value greater thanzero. The motor torque 356 is controlled in a slow ramp, filter functionor other profile through the lash zone 354 until point R1 is reached.The input torque 358 is the sum of the engine torque 352 and the motortorque 354. At point R1, the gear teeth are smoothly meshed, and moretorque can be applied by the motor and/or engine in the negativedirection without a harsh event or oscillation, as shown by the outputtorque 360. Engine torque 352 is allowed to fall to an idle value.

The lash zone crossing control algorithm is shown as a flowchart in FIG.8. The left portion of the flowchart generally shows operation wheredriver demand is increasing, or tip in conditions, and the right portionof the flowchart generally shows the operation while driver demand isdecreasing, or tip out conditions.

The controller 42 begins at block 400, and proceeds to block 402 whereit determines if the input torque, τ_(in), is positive or negative. Ifthe input torque is positive, the controller 42 proceeds to 404, whereit determines if driver demand is decreasing, such as through a tip outevent. If driver demand is decreasing at 404, the controller 42 monitorsthe transmission input torque compared to the lash zone. If thetransmission input torque enters the lash zone at 406, the controller 42determines if the engine 12 is operating and providing torque at 408. Ifthe engine 12 is not operating, which correlates to an electric onlymode of operation for the vehicle, the controller 42 controls thedecrease in motor 14 torque until the lash zone is exited at 412. If theengine 12 is operating at 408, correlating to a hybrid mode for thevehicle, the controller 42 holds the engine 12 torque output constant,or to a steady value at 410, and also controls the decrease in motor 14torque until the lash zone is exited at 412.

If the input torque at 402 is negative, the controller 42 proceeds to414, where it determines if driver demand is increasing, such as througha tip in event. If driver demand is increasing at 414, the controller 42monitors the transmission input torque compared to the lash zone. If thetransmission input torque enters the lash zone at 416, the controller 42determines if the engine 12 is operating and providing torque at 418. Ifthe engine 12 is not operating, which correlates to an electric onlymode of operation for the vehicle, the controller 42 controls theincrease in motor 14 torque until the lash zone is exited at 422. If theengine 12 is operating at 418, correlating to a hybrid mode for thevehicle, the controller 42 holds the engine 12 torque output constant,or to a steady value at 420, and also controls the increase in motor 14torque until the lash zone is exited at 422.

As such, various embodiments according to the present disclosure providefor control of backlash in a driveline when crossing through the lashzone during a vehicle acceleration or deceleration event, such as for atip in or tip out event. The engine and/or the electric machine arecontrolled depending on the operational mode of the vehicle, and basedon a positive or negative input torque to the transmission. For electriconly operation of the vehicle, the torque output of the electric machineis controlled through the lash zone as a ramp, filter function, or otherprofile. For hybrid operation of the vehicle, the torque output of theengine is generally held constant across the lash zone while the torqueoutput of the electric machine is controlled and modulated using a rampor filter function or other profile to reduce lash. Generally the motortorque leads while the engine torque is held generally constant throughthe lash zone to control the input torque and reduce lash.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A vehicle comprising: an engine; a traction motorconnected to the engine by an upstream clutch; a driveline connected toa vehicle wheel, the driveline connected to the traction motor by adownstream clutch; and a controller configured to control traction motortorque through a region surrounding vehicle wheel torque reversal,control driveline input torque during torque reversal of drivelineoutput torque to limit rate of change of driveline output torque, andcontrol traction motor torque during a torque reversal of at least onedriveline component to limit rate of change of the torque applied to thedriveline component when at least one of the upstream and downstreamclutches are locked, the region defined as a function of driveline inputtorque, driveline output torque, nonproportional driveline losses, andan actual torque ratio across the driveline.
 2. The vehicle of claim 1wherein traction motor torque is controlled to a first rate of changebefore the region, and is controlled to a second rate of change throughthe region, the second rate of change slower than the first rate ofchange.
 3. The vehicle of claim 1 wherein the controller is configuredto control engine torque through a region surrounding a vehicle wheeltorque reversal and control engine torque during a torque reversal of atleast one driveline component to limit rate of change of the torqueapplied to the driveline component.
 4. The vehicle of claim 3 whereinthe input torque is based on the traction motor torque and the enginetorque.
 5. The vehicle of claim 3 wherein the vehicle wheel torquereversal is from negative to positive torque; and wherein the enginetorque is held to a generally constant value through the region.
 6. Thevehicle of claim 5 wherein the traction motor torque is controlled to afirst rate of change before the region, and is controlled to a secondrate of change through the region, the second rate of change slower thanthe first rate of change.
 7. The vehicle of claim 3 wherein the vehiclewheel torque reversal is from positive to negative torque; and whereinthe engine torque is held to a generally constant value through theregion.
 8. The vehicle of claim 1 wherein the function isτ_(out)=(τ_(in)*TR_(actual))−T_(s).
 9. A vehicle comprising: a motorpositioned between an engine and a driveline connected to a vehiclewheel; and a controller configured to control motor torque during wheeltorque and driveline component torque reversals to limit a vehicleoutput torque rate of change through a lash region associated with arange of driveline torque ratios each having positive input torque andnegative output torque and bounded by zero driveline input and outputtorque at either end.
 10. The vehicle of claim 9 where the region isbounded at either end by nonzero driveline input torque and nonzerodriveline output torque, respectively.
 11. The vehicle of claim 9wherein the region is bounded at one end by nonzero driveline inputtorque equal to a ratio of nonproportional driveline losses over anactual driveline torque ratio.
 12. The vehicle of claim 9 wherein theregion is bounded at one end by nonzero driveline output torque equal tononproportional driveline losses.
 13. The vehicle of claim 9 wherein theregion is bounded at one end by nonzero driveline input torque and thezero driveline output torque; and wherein the region is bounded atanother end by nonzero driveline output torque and the zero drivelineinput torque.
 14. The vehicle of claim 9 wherein the controller isfurther configured to control engine torque to a generally constantvalue through the region.
 15. The vehicle of claim 9 wherein motortorque is controlled to a first rate of change before the region, and iscontrolled to a second rate of change through the region, the secondrate of change slower than the first rate of change.
 16. The vehicle ofclaim 9 further comprising controlling the motor torque to a specifiedprofile through the region.